removed extended gflow stub

pyzx/gflow.py

@@ -140,60 +140,3 @@ def gflow(
             processed.update(correct)
             k += 1
 
-
-def extended_gflow() -> None:
-    r"""NOT IMPLEMENTED YET: Compute the extended (i.e. 3-plane) gflow of a diagram in graph-like form.
-
-    Based on the algorithm in "There and Back Again"
-    See https://arxiv.org/pdf/2003.01664
-
-    For reference, here is the pseudocode from that paper:
-    ```
-    input: an open graph, given as:
-        - M: an adjancency matrix M
-        - I: input rows/cols
-        - O: output rows/cols
-        - lambda: a choice of measurement plane for each vertex
-    output: extended gflow, given as a triple (success, g, d) where:
-        - g: assigns each vertex its correction set
-        - d: assigns each vertex a "depth", i.e. the number of layers away from the output layer. This
-             is related to the flow ordering as v ≺ w <=> d(v) > d(w)
-
-    EXT_GFLOW(M, I, O, lambda)
-      initialise functions g and d
-      foreach (v in O)
-        d(v) <- 0 // Outputs have depth 0
-      end
-      return GFLOWAUX(M, I, O, lambda, 1, d, g) // Start the recursive process of finding Vj^≺
-    end
-
-    GFLOWAUX(M, I, O, lambda, k, d, g)
-      O' <- O \\ I
-      C <- {}
-      foreach (u in O^⟂)
-        if lambda(u) = XY
-          K' <- Solution for K Δ O' where Odd(K) ∩ O^⟂ = {u}
-        elseif lambda(u) = XZ
-          K' <- {u} ∪ (Solution for K Δ O' where Odd(K ∪ {u}) ∩ O^⟂ = {u})
-        elseif lambda(u) = YZ
-          K' <- {u} ∪ (Solution for K Δ O' where Odd(K ∪ {u}) ∩ O^⟂ = {})
-        end
-        if K' exists
-          C <- C ∪ {u}
-          g(u) <- K'  // Assign a correction set for u
-          d(u) <- k   // Assign a depth value for u
-        end
-      end
-      if C = {}
-        if O = V
-          return (true, g, d)  // Halt, returning maximally delayed g and depth values d
-        else 
-          return (false, {}, {}) // Halt if no gflow exists
-        end
-      else 
-        return GFLOWAUX(M, I, O ∪ C, lambda, k+1, d, g)
-      end
-    end
-    ```
-    """
-    raise ValueError("Not implemented")